Which of the following statements are not correct?

The stability of carbocations follows the order ${\text{CH}}_{\text{3}}^{\text{+}}{\text{\hspace{0.17em}>\hspace{0.17em}CH}}_{\text{3}}{\text{CH}}_{\text{2}}^{\text{+}}\text{\hspace{0.17em}>\hspace{0.17em}}{\left({\text{CH}}_{\text{3}}\right)}_{\text{2}}{\text{CH}}^{\text{+}}\text{\hspace{0.17em}>\hspace{0.17em}}{\left({\text{CH}}_{\text{3}}\right)}_{\text{3}}{\text{C}}^{\text{+}}$

Nucleophilic substitution reaction involving ${\text{S}}_{\text{N}}\text{1}$  mechanism is always associated with the inversion of configuration of carbon atom.  

Nucleophilic substitution reaction involving  ${\text{S}}_{\text{N}}\text{2}$ mechanism is always associated with the  inversion of configuration of carbon atom          

The ${\left({\text{CH}}_{\text{3}}\right)}_{\text{3}}\stackrel{\text{•}}{\text{C}}$ is more stable than   ${\left({\text{CH}}_{\text{3}}\right)}_{\text{2}}\stackrel{\text{•}}{\text{CH}}$